Plastic testing machine



June 30, 1959 w. Goss HAL 2,892,342

PLASTIC TESTING MACHINE Filed im.` 3o. 1954 T F/ .l n'

fm/cwors. Wyman 605s, EV/'o /ndrems, by @.Gd

The/'2^l Attorney States Patent O o o 2,892,342 PLASTIC TEsnNG MACHINEWyman Goss and Eliot R. Andrews, Pittsfield, Mass., 'assgnors to GeneralElectric Company, a corporation h YofNew York y Applicant@ December30,1954, serial No. 478,814 iclaim. (ci. '1s-12) not indicate the`amount ,of energy required to initiatel fracture.

The present invention is an-improvement over modied. fflzodi.typelrnethods inwhich apparatus based on a falling `weightis employed'to determine both the fatigue strengthandfimpactstrength of plastics bymeasuring the energy .necessary to initiate fracture of a standard Izodtypespecimen having -a notch milled in its upper face. In 1this-methodof testing, the specimen is molded by standard procedure lusually of thesame dimensions and must be Aclamped in lposition during testing. Thus,it is notpossible ,tontest specimens of sundry shapes, for example, inthejshape of the iinal molded product. Additionallygtestingmachines'of'thistype are further limited ingthat-they-arenot capable ofmeasuring the hot rigidity offplastiospecimens.

One of the` objects of this invention is to provide a. test machine orapparatus capable of determining the fatigue and impact strengthofplastic specimens of varying thicknesses by measuring the energynecessary to initiate fractura thereof and the energy necessary Vtoproduce failure,l o o jAnother object is toprovide a machine fordeterminingvthe fatigue and impact strength of plastic materials inwhichmeansware provided for supporting the specimen beingtested inamanner having the least tendency to atlect;` thetestresults.

A further-object isto provide a test machine or apparatus for testing.the hot rigidity of plasticmaterials.

vThe. above; and furtherA objects ofthe invention will beapp'arent lfromltheY following .description -taken in connection.,'vvith:theaccompanying drawing in which jFig. 1 is a frontviewpartly in elevation and partly inv section, of an impacttestingmachine of the invention.

.-2 isa section taken on line v2,2 of Fig. 1.

Fig. 3d is afragmentary front elevation View, partly in section, ofv amodification of Fig. l showing a machine or `tester primarily adaptedfor testing the hotrigidity of plastic `specimenvs.

the apparatus includes a base 1 constructed in the form of a hollowcylinder mounted on supports 2. The hollowed'portion 6 extends'throughthe base, theupper part bjein'gfof widerfdiameter in ordcrto receive atest speci- Referring more, particularly to. Fig. 1 of the drawing,

Two upright frame members 7 shown in the form of rectangular bars aremounted on thev base 1. Guide members 8, marked off perpendicularly ininches, are each provided with an elongated slot 9 to permit verticaladjustment between the bars 7 and strips 10 by means of wing nut bolts11. The lowerend ofV each guide member may abut the test specimen whenin place Without exerting any direct weight thereon.

A carrier assembly 12, built on a threaded rod 13 and having a handleportion 14, includes a hemisphere 15 to serve as an instrument ofpercussion. Assembly 12 consists of a rectangular bar 16, slotted tofolloW is a housing 20 for the apparatus which may be providedv withheating or cooling means as required.V Housing 20 has an opening 21 atthe top thereof to receive rod 13. The housing enclosure 20 may also beprovided with a window 24 so that the specimen may be observed andreadings taken.

As illustrated in Fig. 3, the apparatus may be modied to providemeansfor testing the hot rigidity of plastics. This modification mayalso include a housing with appropriate heating means. In the embodimentshown in Fig. v3, a .micrometer 22 is rotatably mounted on one of thesupport members and positioned so that plunger 23 is in direct contactwith the plastic specimen.

While the principle of measuring the eifect of a free falling weight ona specimen is not new, methods employing this principle heretofore havebeen in connection with standard Izod type specimens which cannot bemade to approximate the desired molded article in shape or thickness.Additionally, the energy measurement is .not believed to be accurate inview of energy losses due increments of force in an apparatus whichoffers unrestricted support of thel specimen, simulation of actualimpact conditions and negligible friction. These latter objectives areobtained by means of the rim 4 which is designed so as to support thespecimen -to offer the least possible area of contact therewith. In thismanner, a oating effect is approximated in order to approach theultimate accuracy in determining the energy required to produceincipient cracking and complete failure.

`Fordetermining the impact strength and the fatigue strength of plasticspecimens, the testing machine of the invention is designed so that thecarrier assembly 12 may be raised manually or mechanically to a desiredheight, measured by means of graduated guide members 8, and the weightguided by guides 8 allowed to drop so that the percussion hemispherealways strikes the specimen at the same point. fatigue strength in footpounds by dropping a constant weight from a constant height'untilincipient cracking or outright failure occurs. The number of dropsmultiplied by the product of the height in feet times the weight inpounds employed gives vthe energy required in ft.` lbs. Impact strengthmay be determined by sequentially increasing the height of fall Iof aconstant weight by a constant distance and'ca'lculatingy the cumulativeft. lbs.

Patented June 30, 1959' The machine can be used to measure theA ofenergy required to produce incipient cracking or disintentation.calculation made as follows:

s=%[2a+,(N-1)d] lili??? S=sum of N terms 1 in ft. lbs. N=number of blowsa=force of rst blow (ft. lbs.) d=constant increase of height in ft. lbs.

1 Terms=nuxnber of blows'.

The impact strengths of several general purpose phenolic plasticlspec'i'nijens were determined by sequentially `increasing the'heightoftall of a constant weight .by a constant distance. Threespeoime'ns, 4`inches in diameter and 1A; inch'thick, composed of '(1) a phenolic resinwithl a' woodflour iiller, (2) a' rubberphenolic'with an asbestosfiller, "and (3")l va rubber phenolicl with'arag lle'r were tested using1A, V2' and l lb. weights, respectively. These tests were conducted byst'rting'at an initial drop height of l 4inch and increasing ltlieheight'sequentially by l inch incrementsl until the rst cracl'appeared.For each Vofr" the'three specimens tested, incipientA cracking appearedat' a, final dp'heeht .0f 15 The energy Cab culations for each of thespecimens follow:

Example 1.-'l`est with 1%: 1b. weight:

15 2 1 p 'llpmm ft. ibs. Example 2.-1`est with l lb. weight:

15 .2 1 S degl-.5.0. e lbs- Exqmple 3.-Test withl lb. 15 2 1 ,q [1 2+(14%]*100 ft. 1bs.

As disclosed earlier the fatigue strength of the plastic specimen may bedeterminedV by dropping a constant weight from a constant heightnntilthe rst crack is observed. The energy required to"pr'ifdnce` this crackmay then be calculated by"sirriply multiplying the three factors. Forexample, `the energy required to crack a specimen with a 1/2l weightdropped from a' distance of 1: ft. 'ten times would bel/2 `lr 1r0f=5'.t) ft. lbs.V

The following examples, listed below in Table I, illustrate the use yofthe apparatus to `measure the fatigue strength of plastic specimensf Thesame resin ywas employed in each of .thespecirnens of Examples 7, 8 and9 but the fillers usedwere :three diiere'nt4 grades of rag, identitedasA, B and C, respectively. These examples further illustrate'theladaptability of the apparatusto specimens'of varying thicknesses; TheVenergy required to produce cracking and'complete failure may be readilycalculated, as disclosed'previous'ly, by merely multiplying thenumber ofdropsby theheight of fall by the weight employed.

Table I y Disk Fatigue, No. of

Thlck- Drop Hammer Drops Specimen l ness Feet Weight, D cpth, Lbs.

inchesk t Crack Fall Rubber-phenolic wood hour filler .123 2 M 10 44Rubber-phenolic rag filler. 170` 2 1 67 304 Laminate, Grade Ch". .062 21 5 Phenolic, ragllerA. 138 2 3 8l Phenolic, rag filler B. .143 2 7 18Phenolic, rag filler C .139 2 M 8 124 1 Specimen`=4 diameter disks.

The present invention also offers a new, practical, systematic andprecise method oftesting the hot rigidity of plastic material. Ilfhischa'racteristic'has been determined in. the Past by Several @#11945inf'whih ma@ visual indications of this property are obtained. Forexample, one method previously employed merely vi11- volves squeezing aspecimen disk by hand to get comparative hot rigidity characteristicsand obviously can result only in very crude observations. Another methodfrequently used involves the clamping of a standard specimen disk onto asolifl surface with half or two-thirds of the disk projectingover"'tlie"edge of the solid surface. Weights are hung on theprojectedportion of the disk and the resulting degree of deflectionmeasured. Since each of. these methods is subject to the limitations ofthey persons performing the tests'andA since visual obseryatigns are atbest based on individual opinion, results obtained by thesemethods'obviously lmay vary'from one tester to another and cannot always'be relied upon to be accurate for subsequent 'samples of the samematerial.

Still another method of testing the hot rigidity of plastic materials isal so-called heat `distoition ytestin vvh'icfha. 5"- 1/2"' 1/z barspecimen is molded, cooled tofrooml temperature and thensubjected"toaf'standard AS'IM heatY distortionk test which involves theyprocdlir'ie of placing the bar inA a receptacle surrounded by oil,apply# ing weights to the center of lthe bar and raising' theftem-Iperatureof the oil bath' until the rmolded 'bafrfsh'o'w's some since `itinvolves the periods of/colihgt'r'oom temperature and reheating" to adistortion 'temperatre- Additionally, since the specimen is' rectangularand'ftlie weights are placed on its center, thel measurement isVactually limited to a measure of the parallel forcessinc the stresslines form a catenary, 'i l The hot rigidity test which 'maybe conductedby means of the apparatus of this inventionpermits of `a newandpractical method of accurately determining this property' ofhot plasticspecimens'. This isan important property of materials of this type andAmust be accurately determined in view of present molding methods. Forexample, in injection molding, the moldedpie'cesmust be capable of beingremoved trom the moldat 'a t'e'npei'ture 'p proximating the moldingtemperature, that'isfa'tarela-r tively high temperature; In practice,so-'call'ed knockout pins eject the molded'part and if the molded partisnot suiciently rigid at the temperature at which itisy ejected,

deformation will occur andinferior products willI result."

By the present method, it is possibleaccrately te determinethisparticular property'fo 'materials of varying* compositions. In'otherwords, i't'is possibleA measure, this property for a complete line ofplastic materials and to assign these materials 1to end moldinguseswher'e particular property is extremely important-.l

When employed tol test'thehot ofplastic specilmens, the apparatus ofthis invention modified' in accordance with Fig. 3 is used so thatmicrometerzzfrotatably mounted on one of the leg members'zfisposition'edwith its pointer in direct contact with thcl'un'der of a plasti'cmdiskspecimen tobe testedy withl the indicator of the micrometer zeroedas astarting position. In actual practice, a test specimen is vremoved fromthe moldand transferred to the'tester as rapidly as possible.v Tempera'-ture conditions during the test are maintained as close as possible tothe lmolding temperature means yof the.

enter into the calculation'of :this property.' 'Howekjvenit' isimportant in establishing this particular property for the same lineofl'plasticy materialsy that inl every 'test the same weight be appliedin order to have standardized WSUIS, Similarly, the time intervalbetweenl remgying the specimen from the mold and applying the weightmust be a constant for all specimens tested and the period between whichsuch readings are taken must also be standardized and be constant foreach reading.

The method of testing the hot rigidity of plastic specimens afforded bythe apparatus herein described oiers substantial advantages. Forexample, it permits the use of standard disk specimens as the testingspecimens. Additionally, the apex of the applied weight distorts thedisk into a conical form as a result of which the applied force isdistributed proportionately and concentrically from the point of stress.Moreover, the disk permits of another dimension to be represented by abending moment not measured by rectangular shapes whose stress linesform a catenary, as mentioned previously.

The following examples, listed below in Table II, are given toillustrate the use of the apparatus of this invention to determine thehot rigidity of plastic specimens. This may best be illustrated byemploying as test specimens two similar phenolic resins having a woodllour liller, one having added thereto additional lime and additionaliron oxide pigment and the other having neither of these additionaladditives. These specimens were selected for the purpose of determiningwhether or not the test results would show improved hot rigidity for thespecimen containing the additives since these materials are commonlyused for this purpose. In each of these tests, the specimens wereremoved from the mold and transferred to the apparatus as quickly aspossible, the temperature within the housing being adjusted toapproximate the molding temperature. Readings were taken at intervals offorty-tive seconds, sixty seconds and ninety seconds, respectively.

Table ll Rlgidity in Mils Example Specimen l 45 Sec. 60 Sec. 90 See.

phenolic, wood flour ller 155 122 111 11 phenolic, wood our, lime and142 117 86 iron oxide additives.

1 Bpecimen=4 diameter disks.

.The foregoing results show the expected improvement in hot rigidity ofthe specimen containing the additional lime and iron oxide. From this,it is evident that the test method is reliable and can be employed togive reliable results. It is also evident that by this method it ispossible to establish and standardize this property for varyingformulations and to assign products to end uses requiring apredetermined hot rigidity value. Examples 10 and 11 were repeated withsimilar disks with little or no variation in result.

When used to determine hot rigidity the apparatus of this inventionmakes possible a systematic method, heretofore not available ofdetermining and standardizing this property for various formulations.Additionally, the advantages inherent in the apparatus when employed todetermine impact strength and fatigue strength are substantial. One ofthe more important advantages is that smaller diierences are detectablebetween the values of lots or types of products than with any otherapparatus available. This may be attributed to the design of theapparatus, particularly the narrow rim employed to support the specimen,making possible the application of small increments of force which,coupled with unrestricted support of the specimen, results in negligiblefriction and simulation of nearly actual impact conditions. Otherimportant advantages are the simplicity of the apparatus, its specificadaptability to plastics, its simple operation and low cost.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

In a machine for testing the impact and fatigue strength of moldedplastic material, means for supporting gravitationally a test specimenof plastic material comprising a recessed rim containing a raisedannular portion substantially narrower than said rim and upon which saidspecimen is supported so that the upper surface and substantially theentire lower surface of the test specimen are free of contact with saidsupporting means while at the same time the specimen is confned in arelatively xed position, a carrier assembly adapted to apply a variableload to said specimen, said carrier assembly comprising a terminalhemisphere for striking the specimen at a central portion thereof, saidcarrier assembly being freely movable in a vertical direction, means forguiding the carrier assembly so that the hemisphere strikes the testspecimen at a point equidistant from its position of support and meansintegral with said guide means for measuring the height of fall of saidcarrier assembly.

References Cited in the tile of this patent UNITED STATES PATENTS1,071,430 Keen Aug. 26, 1913 1,498,659 Jackson June 24, 1924 1,709,638Thwing Apr. 16, 1929 1,830,842 Vercombe Nov. 10, 1931 1,985,478 YuasaDec. 25, 1934 2,388,246 Berger Nov. 6, 1945 2,479,984 Stock Aug. 23,1949 2,579,503 Lubin Dec. 23, 1951 2,748,596 Tasker June 5, 1956 FOREIGNPATENTS 248,888 Great Britain Mar. 18, 1926

